1. Field of the Invention
This invention relates to a navigation apparatus which displays a travel route of a moving object such as a vehicle and famous buildings or place names around the route together with map thereby to assist the movement of the moving object. More specifically, this invention relates to a bird""s-eye-view display of the map information in such a navigation apparatus.
2. Description of the Prior Art
Recently, there is known a navigation apparatus as a position measurement apparatus for a moving object such as a vehicle, an airplane and a vessel. The navigation apparatus generally displays a position mark of the moving object with a map around the vehicle position so as to guide the driver to the destination. The navigation apparatuses installed in a vehicle are roughly classified into two types: a stand-alone type navigation apparatus and a GPS (Global Positioning System) navigation apparatus. A stand-alone type navigation apparatus derives the travel direction data and the travel distance data of the vehicle by means of a speed sensor and an angular velocity sensor installed in the vehicle, successively adds those data to a reference position to calculate the current position of the vehicle, and then displays the map with the position mark of the vehicle on a display device based on the current position thus calculated. On the other hand, a GPS navigation apparatus receives measurement radio waves from a plurality of GPS satellites launched into space via a GPS receiver, calculates the current position of the vehicle from the received data using a three- or two-dimensional measurement method, and then displays the current position mark and map on a display device.
Nowadays, a so-called hybrid type vehicle navigation apparatus, which has functions of both the stand-alone type and the GPS type navigation apparatus, is known. Further, some navigation apparatuses are capable of displaying a preset travel route of the vehicle on a map together with names of buildings or places located around the preset travel route. Those navigation apparatuses enable the user (driver) to recognize the current position of the vehicle in connection with the map around there so that the user can readily and safely reach the destination without losing the way, even if he or she goes there for the first time.
In those navigation apparatuses, a so-called bird""s-eye-view display of the map had been employed recently, so as to enlarge the range of displayed map and achieve more natural and real map display. The bird""s-eye-view display is a map display method which shows the map as if the user is viewing the area obliquely downwardly from a midair viewing position (namely, displays a map in a one-point perspective projection view from a midair view point). The bird""s-eye-view display is generally broadly used in a flight simulator, for example.
The conventional vehicle navigation apparatus having the bird""s-eye-view display function generally converts the map including roads together with characters to be displayed in the map (for example, the place name display of the target places and route display of the route points to be passed by) into the bird""s-eye-view diagram and displays it. Namely, not only the map but characters or marks associated with the map are shown in the bird""s-eye-view manner. However, in such cases, it is difficult to show certain character string on the travel route which is of special importance, such as the target objects to which the driver""s attention should be paid, in a manner distinguished from the other characters.
It is an object of the present invention to provide a map information display device for use in a vehicle navigation apparatus having a bird""s-eye-view display function, which is capable of displaying some important targets and the like, to which the driver""s attention should be paid, in a distinguished manner.
According to one aspect of the present invention, there is provided a map information display device for use in a navigation apparatus which displays map to assist a travelling of a moving object, the device including: a map data extracting unit for extracting character data corresponding to characters from map data corresponding to the map; a map data converting unit for converting the map data including no character data to a bird""s-eye-view map data; a character data converting unit for selecting designated character data from the extracted character data and for converting the character data other than the designated character data to birds-eye-view character data; a combining unit for combining the bird""s-eye-view character data, the bird""s-eye-view map data and the designated character data to produce combined bird""s-eye-view data; and a display unit for displaying the map of bird""s-eye-view using the combined bird""s-eye-view data.
In accordance with the map information display device thus configured, the map data extracting unit extracts character data corresponding to characters from map data corresponding to the map, and the map data converting unit converts the map data including no character data to a bird""s-eye-view map data. The character data converting unit selects designated character data from the extracted character data and converts the character data other than the designated character data to bird""s-eye-view character data. Then, the combining unit combines the bird""s-eye-view character data, the bird""s-eye-view map data and the designated character data to produce combined bird""s-eye-view data. Then, the display unit displays the map of bird""s-eye-view using the combined bird""s-eye-view data.
As a result, the designated data are not shown in the birds-eye-view manner differently from the other character data which are shown in the bird""s-eye-view fashion. Therefore, those designated characters are distinguished from other characters on the displayed map, and the user can easily recognize those designated characters.
In a preferred embodiment, the designated character data may be designated by a user in advance. Alternatively, the designated character data may be designated in accordance with one of the following: an area where the moving object is travelling, a current time of the moving object, a travelling direction of the moving object, or a traffic information supplied from an external unit.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiment of the invention when read in conjunction with the accompanying drawings briefly described below.